Exposure to moderately high temperature enables plants to acquire thermotolerance to high temperatures that might otherwise be lethal. In , histone H3 lysine 27 trimethylation (H3K27me3) at the () and loci is removed by Jumonji C domain-containing protein (JMJ) histone demethylases, thus allowing the plant to 'remember' the heat experience. Other heat memory genes, such as are downregulated in acclimatized quadruple mutants compared to the wild type, but how those genes are regulated remains uncharacterized. Here, we show that histone H3 lysine 4 trimethylation (H3K4me3) at was maintained at high levels for at least three days in response to heat. This heat-dependent H3K4me3 accumulation was compromised in the acclimatized quadruple mutant as compared to the acclimatized wild type. JMJ30 directly bound to the locus in response to heat and coordinated H3K27me3 and H3K4me3 levels under standard and fluctuating conditions. Our results suggest that JMJs mediate the balance between H3K27me3 and H3K4me3 at the locus through proper maintenance of H3K27me3 removal during heat acclimation.